Linux文件操作例子

1. 读文件的代码

int main(int arg, char *args[])
{
if (arg < 2)
return 0;
int fd = open(args[1], O_RDONLY); //只读方式打开文件abc.txt
if (fd == -1)
{
printf("error is %s\n", strerror(errno)); //知道更加详细的错误信息
} else
{
printf("success fd = %d\n", fd);
char buf[100];
memset(buf, 0, sizeof(buf));
while(read(fd, buf, sizeof(buf) - 1) > 0)//循环读取文件内容，直到文件结尾，退出循环
{
printf("%s\n", buf);
memset(buf, 0, sizeof(buf));
}
close(fd); //一个文件描述符用完后一定要用close()函数关闭
}
return 0;
}

2. 写文件的代码

int main(int arg, char *args[])
{
char s[] = "abc.txt";
int fd = open(s, O_RDWR | O_APPEND);//用读写追加方式打开文件
if (fd == -1)
{
printf("error is %s\n", strerror(errno));
}else
{
printf("success fd = %d\n", fd);
char buf[100];
memset(buf, 0, sizeof(buf));
strcpy(buf, "hello world\n");
int i = write(fd, buf, strlen(buf));//这里要用strlen函数
close(fd);
}
return 0;
}

3. 得到文件状态代码
int main(int arg, char *args[])
{
int fd = open(args[1], O_RDONLY);
if (fd == -1)
{
printf("error is %s\n", strerror(errno));
}else
{
printf("success fd = %d\n", fd);
struct stat buf;
fstat(fd, &buf);  //使用fstat获取文件信息
if (S_ISREG(buf.st_mode))//判断文件是否为标准文件，S_ISREG是系统定义的宏，计算stat接口的st_mode成员。
{
printf("%s is charfile\n", args[1]);
}
if (S_ISDIR(buf.st_mode))//判断文件是否为目录
{
printf("%s is dir\n", args[1]);
}
printf("%s size =%d\n", args[1], buf.st_size);//得到文件大小
close(fd);
}
return 0;
}

4. C库函数读取文件的代码
int main(int arg, char *args[])
{
FILE *p = fopen(args[1], "r+");
if (p == NULL)
{
printf("error is %s\n", strerror(errno));
}else
{
printf("success\n");
char buf[100];
size_t rc = 0;
while(1)                              
{                                                  
size_t tmp = fread(buf, 1, sizeof(buf), p);//原则是第二个参数乘以第三个参数的大小不能超过缓冲区
rc += tmp;
if (tmp == 0)
break;
}
printf("rc = %d\n", rc);  
fclose(p);
}
return 0;
}

5. c库函数读写二进制文件的代码
struct person
{
int id;
char name[20];
int age;
int sex;
char tel[20];
};


int main(int arg, char *args[])
{
FILE *p = fopen(args[1], "w");  //在Windows系统下，读二进制文件时，"w"改为"wb"
if (p == NULL)
{
printf("error is %s\n", strerror(errno));
} else
{
printf("success\n");
struct person man;
memset(&man, 0, sizeof(man));


while(fread(&man, sizeof(struct person), 1, p)) //fread适合读二进制文件
{
printf("id=%d\n", man.id);
printf("name=%s\n", man.name);
printf("age=%d\n", man.age);
printf("tel=%s\n", man.tel);
}
fclose(p);
}
return 0;
}


int main(int arg, char *args[])
{
FILE *p = fopen(args[1], "w");
if (p == NULL)
{
printf("error is %s\n", strerror(errno));
} else
{
printf("success\n");
struct person man[10];
memset(&man, 0, sizeof(man));


man[0].id = 0;
strcpy(man[0].name, "择聂思");
man[0].age = 50;
man[0].sex = 1;
strcpy(man[0].tel, "911");


man[1].id = 1;
strcpy(man[1].name, "择特谁");
man[1].age = 20;
man[1].sex = 0;
strcpy(man[1].tel, "119");


fwrite(&man, sizeof(struct person), 2, p);
fclose(p);
}
return 0;
}


6. 写log的代码
void writelog(const char *log)
{
time_t tDate;
struct tm *eventTime;
time(&tDate);//得到系统当前时间
eventTime = localtime(&tDate);//将time_t数据类型转化为struct tm结构
int iYear = eventTime->tm_year + 1900;
int iMon = eventTime->tm_mon + 1;
int iDay = eventTime->tm_mday;
int iHour = eventTime->tm_hour;
int iMin = eventTime->tm_min;
int iSec = eventTime->tm_sec;


printf("tm_isdst = %d\n", eventTime->tm_isdst);


char sDate[16];
sprintf(sDate, "%04d-%02d-%02d", iYear, iMon, iDay);
char sTime[16];
sprintf(sTime, "%02d:%02d:%02d", iHour, iMin, iSec);
char s[1024];
sprintf(s, "%s %s %s\n", sDate, sTime, log);
FILE *p = fopen("my.log", "a+");
if (p == NULL)
{
printf("write log my.log error:%s\n", strerror(errno));
}else
{
fputs(s, p);
fclose(p);
}
return;
}

7. 读目录的代码
int main(int arg, char *args[])
{
if (arg <2)
return 0;
DIR *dp;
struct dirent *dirp;
dp = opendir(args[1]);//打开目录文件
if (dp == NULL)
{
printf("error is %s\n", strerror(errno));
return 0;
}
while((dirp = readdir(dp)) != NULL)//用readdir循环读取目录内容，读到目录尾，循环break
{
printf("%s\n", dirp->d_name);//将目录下的文件名打印到屏幕
}
closedir(dp);//关闭目录
return 0;
}